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United States Patent |
5,328,982
|
Tindall
,   et al.
|
July 12, 1994
|
Depolymerization of substantially amorphous polyesters
Abstract
Ester bonds are hydrolyzed in the conversion of substantially amorphous
polyesters to their monomeric components, by being contacted with a
mixture of (a) an alcohol, such as methanol, or glycol, (b) a polar
aprotic solvent such as N-methyl-pyrrolidone or dimethyl sulfoxide and (c)
an alkoxide or hydroxide such as sodium hydroxide.
Inventors:
|
Tindall; George W. (Kingsport, TN);
Perry; Randall L. (Bluff City, TN);
Spaugh, Jr.; Art T. (Kingsport, TN)
|
Assignee:
|
Eastman Chemical Company (Kingsport, TN)
|
Appl. No.:
|
970220 |
Filed:
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November 2, 1992 |
Current U.S. Class: |
528/488; 134/29; 528/481; 528/489; 528/493; 528/497; 528/503; 560/78; 560/79; 562/483; 562/485 |
Intern'l Class: |
C08J 003/00 |
Field of Search: |
528/481,488,489,493,497,503
134/29
562/483,485
560/78,79
|
References Cited
U.S. Patent Documents
3120561 | Feb., 1964 | Chambret | 562/483.
|
3952053 | Apr., 1976 | Brown, Jr. et al. | 562/483.
|
4078143 | Mar., 1978 | Malik et al. | 560/78.
|
4163860 | Aug., 1979 | Delattre et al. | 560/96.
|
4355175 | Oct., 1982 | Puszkaszeri | 562/483.
|
4542239 | Sep., 1985 | Lamparter et al. | 562/487.
|
4578502 | Mar., 1986 | Cudmore | 560/79.
|
4605762 | Aug., 1986 | Mandoki | 562/483.
|
4620032 | Oct., 1986 | Doerr | 562/483.
|
4876378 | Oct., 1989 | VanSickle | 560/78.
|
5045122 | Sep., 1991 | Tindall et al. | 134/29.
|
Foreign Patent Documents |
453369 | Jan., 1965 | JP.
| |
Other References
Anal. Chem. 34 (1962) 1173 G. G. Esposito.
Anal. Chem. 37 (1965) 1709 J. Jankowski & P. Garner.
Anal. Chem. 37 (1965) 1306, J. R. Kirby, A. J. Baldwin and R. H. Heidner.
Anal. Chem. 264 (1973) 293, D. Vink, R. van Wijk.
J. Appl. Poly. Sci. 18 (1974) 1953 D. Nissen, V. Rossbach, and H. Zahn.
Anal. Chem. 34 (1962) 1048 G. G. Esposito and M. H. Swann.
Makromol Chem. 77 (1964) 153 R. Janssen, H. Ruysschaert, and R. Vroom.
J. Oil Col. Chem. Assoc. 50 (1967) 373 J. Rawlinson and E. L. Deeley.
J. Chromatogr. 351 (1986) 203 P. Perlstein and P. Orme.
Anal. Chem. 47 (1975) 1708 J. C. West.
Anal. Chem. 40 (1968) 229 L. H. Ponder.
Anal. Chem. 49 (1977) 741 B. J. Allen, G. M. Elsea, K. P. Keller and H. D.
Kinder.
J. Am. Chem. Soc. 83 (1961) 117 J. Miller and A. J. Parker.
Talanta 13 (1966) 1673 J. A. Vinson, J. S. Fritz and C. A. Kingsbury.
Physical Organic Chemistry, Longmin Scientific and Technical, Longman Group
UK Limited, Essex, England, N. Issacs.
|
Primary Examiner: Acquah; Samuel A.
Attorney, Agent or Firm: Montgomery; Mark A.
Claims
What is claimed is:
1. A process for the conversion of polyesters to their monomeric components
comprising contacting a substantially amorphous polyethylene terephthalate
having a crystallinity of no greater than 25% with a mixture of (a) at
least one alcohol or glycol; (b) at least one polar aprotic solvent; and
(c) at least one alkoxide or hydroxide for a sufficient time to convert at
least a portion of said polyester to it's monomeric components; wherein
said alcohol or glycol, said polar aprotic solvent, and said alkoxide or
hydroxide are compatible, bringing at least a portion of said alkoxide or
hydroxide into solution in the solvent mixture.
2. The process according to claim 1 wherein the amount of component (a) is
between about 5 and 80 volume % and the amount of component (b) is between
about 95 and 20 volume %.
3. The process according to claim 2 wherein component (c) is in a
concentration between 0.5 molar and saturated condition in the solvent
mixture of components (a) and (b).
4. The process according to claim 1 wherein said substantially amorphous
polyethylene terephthalate i in particulate form.
5. The process according to claim 1 wherein said alcohol is selected from
the group consisting of C1 to C4 alcohols; said glycol is ethylene glycol;
said polar aprotic solvent is selected from dimethyl formamide, dimethyl
sulfoxide, sulfolane, hexamethyl-phosphoramide, and N-methylpyrrolidone;
said alkoxide is elected from the group consisting of C.sub.1 to C.sub.4
alkoxides; and said hydroxide is selected from the group consisting of
alkali metal hydroxides, alkaline-earth metal hydroxides, tetra-alkyl
ammonium hydroxide, and ammonium hydroxide.
6. The process according to claim 1 wherein said alcohol or glycol is
selected from the group consisting of C.sub.1 to C.sub.4 alcohols.
7. The process according to claim 6 wherein said alcohol or glycol is
methanol; said polar aprotic solvent is selected from dimethyl sulfoxide
and N-methylpyrrolidone; and said alkoxide or hydroxide is selected from
the group consisting of sodium hydroxide, potassium hydroxide or tetra
alkyl ammonium hydroxide.
8. The process according to claim 1 wherein said substantially amorphous
polyethylene terephthalate is contacted with said mixture at a temperature
between about room temperature and about 200.degree. C.
9. The process according to claim 8 wherein said substantially amorphous
polyethylene terephthalate is contacted with said mixture at about room
temperature.
10. The process according to claim 1 wherein said mixture is in
substantially anhydrous conditions.
11. The process according to claim 1 wherein said alkoxide or hydroxide is
dissolved in said alcohol or glycol prior to the addition of said polar
aprotic solvent.
12. The process according to claim 1 wherein said alkoxide or hydroxide is
present in a molar excess with respect to ester bonds in said
substantially amorphous polyethylene terephthalate.
13. The process according to claim 1 further comprising, prior to said
contacting, heating a crystalline polyethylene terephthalate to form a
melt and quenching said melt into a liquid to form a substantially
amorphous polyethylene terephthalate.
14. The process according to claim 13 wherein said liquid is at least one
component of said mixture of (a), (b) and (c).
15. A process for the conversion of polyesters to their monomeric
components comprising:
I) heating a crystalline polyethylene terephthalate to form a melt,
II) quenching said melt to form a substantially amorphous polyethylene
terephthalate having a crystaliniity no greater than 25%, and
III) contacting sad substantially amorphous polyethylene terephthalate with
a mixture of (a) about 5 to 80 (vol) % methanol, (b) about 95 to 20 (vol)
% of a polar aprotic solvent selected from the group consisting of
dimethyl sulfoxide and N-methyl-pyrrolidone, and (c) an alkali metal
hydroxide in molar excess, with respect to the ester bonds to be
hydrolyzed, at a temperature between about room temperature and the
boiling point of the mixture for a sufficient time to convert said
substantially amorphous polyethylene terephthalate to its monomeric
components.
16. A process for the conversion of polyesters to their monomeric
components comprising:
A) heating crystalline polyethylene terephthalate to form a melt, and
B) quenching said melt into a liquid to form a substantially amorphous
polyethylene terephthalate having a crystallinity no greater than 25%,
wherein said substantially amorphous polyethylene terephthalate is
contacted with a mixture of (a) about 5 to 80 (vol) % methanol, (b) about
95 to 20 (vol) % of a polar aprotic solvent selected from the group
consisting of dimethyl sulfoxide and N-methyl-pyrrolidone, and (c) an
alkali metal hydroxide in molar excess, with respect to the ester bonds to
be hydrolyzed, in said polyethylene terephthalate and said liquid is at
least one component of the mixture of (a), (b) and (c).
Description
FIELD OF THE INVENTION
The present invention relates to the recovery of monomeric components from
polyesters by a hydrolysis process. More particularly the present
invention relates to the hydrolysis of amorphous polyesters.
BACKGROUND OF THE INVENTION
The conversion of acids and alcohols to esters is well known, as is the
conversion of esters to acids and alcohols. The conversion of many esters
to acids and alcohols can be carried out by boiling the ester in a mixture
of base and alcohol. However, the conversion of polyesters to their
corresponding monomeric acids and glycols is very difficult. Polyesters
are normally not soluble in the solvents that are used for the conversion
of esters to alcohol and acid. Also, polyesters are often highly
crystallized, further limiting their solubility and hindering the attack
of the ester bonds by a base.
Methods are known for the conversion of some polyesters to their monomeric
components. These depolymerization methods are generally used to recover
monomers from polymer scrap for the repolymerization of the monomers, but
can also be used to analyze the polymers to determine their monomer
content.
Polyesters can be converted or depolymerized to amides and glycols by a
process known as aminolysis. This process entails the refluxing of a
polyester with a primary amine or hydrazine such as disclosed in ASTM
Method D 2456 and, Anal. Chem. 34 (1962)1173 G. G. Esposito. However, the
aminolysis process is generally slow and produces undesirable side
reactions with some polyesters.
The transesterification of polyesters is another method of depolymerizing
polymers. This method entails heating a polyester in excess alcohol or
glycol, optionally in the presence of a catalyst such as disclosed in ASTM
Method D 2455 and in Anal. Chem. 37 (1965)1709 J. Jankowski and P. Garner.
The transesterification process, however, is generally very slow and high
temperatures and pressures are needed to achieve practical conversion
rates.
Another method of depolymerizing polyesters is by hydrolysis. This process
entails the heating of a polyester with a base in the presence of a
solvent, such as an alcohol, such as disclosed in Anal. Chem. 37
(1965)1306, J. R. Kirby, A. J. Baldwin, and R. H. Heidner; U.S. 4,605,762,
and U.S. 4,620,032. Hydrolysis, however, is also generally slow at mild
conditions, thus, requiring high temperatures and pressures to achieve
rapid conversions.
In spite of the many known depolymerization processes, polyesters are not
easily depolymerizable by any known process at ambient conditions.
In light of the above, it would, therefore, be very desirable to rapidly
convert polyesters under relatively mild conditions of temperature and
pressure without generating undesirable side reactions.
SUMMARY OF THE INVENTION
The process of the present invention rapidly depolymerizes substantially
amorphous polyesters under relatively mild conditions without generating
undesirable side reactions by using a composition comprising a mixture of
(a) alcohol or glycol, (b) polar aprotic solvent, and (c) alkoxide or
hydroxide. The alkoxide or hydroxide, the alcohol or glycol, and the polar
aprotic solvent should be compatible so that the alkoxide or hydroxide
will substantially dissolve at relatively high concentrations in the
solvent mixture.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows the hydrolysis times, at room temperatures, of polyethylene
terephthalate at various percents of crystallinity as measured by
differential scanning calorimetry.
FIG. 2 shows the hydrolysis times, at reflux temperature, of polyethylene
terephthalate at various percents of crystallinity using a conventional
hydrolysis solution.
DETAILED DESCRIPTION OF THE INVENTION
We have surprisingly found that substantially amorphous polyesters are
rapidly converted to their monomeric components by contacting them with a
mixture of (a) at least one alcohol, such as methanol, or glycol, (b) at
least one polar aprotic solvent such as N-methylpyrrolidone or dimethyl
sulfoxide, and (c) at least one alkoxide or hydroxide wherein the alcohol
or glycol is capable of dissolving the alkoxide or hydroxide and this
solution is in turn soluble in the polar aprotic solvent.
The process of the present invention is particularly useful for the
depolymerization or conversion to monomeric components of substantially
amorphous polyesters, including copolymers, mixtures thereof and blends of
these with other polymers. Highly crystallized polyesters are the most
difficult polyesters to depolymerize. However, the process of the present
invention depolymerizes these polyesters quite rapidly by converting them
to substantially amorphous polyesters by melting and quenching.
We have discovered that the mixture of reagents according to the present
processes will hydrolyze substantially amorphous polyesters at
extraordinary rates. At crystallinities below about 25 %, the rate is
especially fast. Thus the present invention preferably entails the
hydrolysis of substantially amorphous polyesters by the process comprising
contacting a polyester having a crystallinity percent of no more than
about 25% with a compatible mixture of (a) at least one alcohol, (b) at
least one polar aprotic solvent, and (c) at least one alkoxide or
hydroxide.
According to the process of the present invention, the hydrolysis of
polyesters having this low of a crystallinity proceeds rapidly and
quantitatively when stirred at atmospheric pressure and ambient
temperature. The hydrolysis of amorphous polyesters according to the
present invention can easily be completed in less than 60 minutes at
ambient conditions with pellets with dimensions between 2 and 3 mm and
much faster at elevated temperatures and/or at reduced particle sizes.
Polyesters can be made amorphous by melting followed by rapid cooling. A
practical way to accomplish this is by passing the material through an
extruder and quenching the molten polymer in some liquid. The quench
liquid could be the hydrolysis reagent mixture or one of its components.
In this way, the heat from the molten polymer could be used to warm the
hydrolysis reagent mixture and speed the reaction.
A preferred process of the present invention comprises:
I) heating a crystalline polyester to form a melt,
II) quenching said melt to form a substantially amorphous polyester, and
III) contacting said substantially amorphous polyester with a mixture of
(a) about 5 to 80 (vol) % methanol, (b) about 95 to 20 (vol) % of a polar
aprotic solvent selected from the group consisting of dimethyl sulfoxide
and N-methylpyrrolidone, and (c) an alkali metal hydroxide in molar
excess, with respect to the ester bonds to be hydrolyzed, at a temperature
between about room temperature and reflux conditions for a sufficient time
to convert said substantially amorphous polyester to its monomeric
components.
We have unexpectedly discovered that polyesters, such as polyethylene
terephthalate, have dramatically improved hydrolysis times when the
crystallinity of the polyester is not much higher than about 25%. As shown
in FIG. 1 polyethylene terephthalate is rapidly hydrolyzed at
crystallinities below 30%, even at ambient conditions. The dramatic
reduction in hydrolysis time commences at low crystallinities of about 27
or 26%. At crystallinity percents below this, the hydrolysis rate is
essentially as fast as for fully amorphous material.
Although we believe that the present invention is useful for the
depolymerization of any substantially amorphous polyester, examples of
suitable polyesters that can be depolymerized by the process of the
present invention include: polyethylene terephthalate; polyethylene
2,6-dinaphthalate; and polymers that are prepared from one or more of the
following monomers, or esters of these monomers; succinic acid, sebacic
acid, azelaic acid, adipic acid, dimer acid, glutaric acid,
trans-1,4-cyclohexanedicarboxylic acid,
cis,trans-1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic
acid, isosebacic acid, carbonic acid, pimelic acid, dimethylmalonic acid,
suberic acid, 1,12-dodecanedioic acid, terephthalic acid, isophthalic
acid, p,p'-methylenedibenzoic acid, 2,6-naphthalenedicarboxylic acid,
phthalic acid, dimethy15-[4-(sodiosulfo)-phenoxy]isophthalate, dimethyl
5-(sodiosulfo)isophthalate, 4,4'-sulfonyldibenzoic acid,
2-(sodiosulfo)-9,9-fluorenebis[propionic acid],
5-[4-(sodiosulfo)-phenoxy]isophthalic acid,
5-[(sodiosulfo)propoxy]-isophthalic acid, trimellitic acid, 4,4'-stilbene
dicarboxylic acid, resorcinol bis acetic acid, 4,4'-biphenyl dicarboxylic
acid, ethylene glycol, 1,3-trimethylene glycol, 1,4-butanediol,
1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol,
1,4-cyclohexanedimethanol, bisphenol A,
2,2,4,4-tetramethyl-1,3-cyclobutanediol, 4,4'-(2-norbornylidene)diphenol,
4,4'-(Hexahydro-4,7-methanoindan-5-ylidene)diphenol,
4,4'-[(3-methyl-2-norbornyl)methylene]diphenol,
4,4'-(2-Norbornylidene)bis(2,6-dichlorophenol),
4,4'-(2-norbornylmethylene)diphenol,
5,6,7,8,-tetrahydro-l,4-naphthalenediol, hydroquinone, t-butyl
hydroquinone, diethylene glycol, glycerin, trimethylol propane,
trimethylol ethane, poly(tetramethylene glycol), poly(propylene glycol),
tischenko glycol, 2,2'-[isopropylidene(p-phenyleneoxy)]diethanol,
poly(ethylene glycol)(carbowax) (any molecular weight), poly(oxyethylene
oxypropylene) (pluronics) (any molecular
weight),4-(hydroxymethyl)cyclohexanecarboxylic acid, hydroxypivalic acid,
6-hydroxyhexanoic acid, and p-hydroxybenzoic acid. The most preferred
polymer, however, due to its wide spread use and emphasis on its recycle
is polyethylene terephthalate.
The process of the present invention is useful in the analysis of the
monomer content of these polyesters; the recovery of monomers from
polyester scrap such as bottles, trays, fibers, etc.; and the removal of
polyester from coated substrates such as dirty polyester processing
equipment. The process of the present invention is useful for the
depolymerization of substantially amorphous polyesters in whatever form,
and crystalline polyesters that can be rendered substantially amorphous.
Though the grinding step is not necessary, smaller polyester particles
have a larger surface area and are much more rapidly converted to the
monomers. Therefore, the particulate form of polyester is more preferred.
The process of the present invention can be conducted at room temperature
under mild conditions. However, increased temperature as with increased
agitation does reduce conversion time. The upper temperature limit is
determined by the capability of the equipment and stability of the
products and should not be so high as to decompose the products. The
process of the present invention is preferably conducted at a temperature
between about room temperature and 200.degree. C., with a temperature at
or near room temperature being most preferred. The upper limit of the
temperature of the conversion process is dependent upon the reactant
materials when the conversion is conducted at refluxing conditions because
the temperature is limited by the boiling temperature of the mixture. We
have found that as the molecular weight of the alcohol or glycol increases
the reflux temperature increases, however, the solubility of the alkoxide
or hydroxide in the final solution decreases which tends to reduce the
rate of reaction.
The process of the present invention is preferably conducted at atmospheric
pressure. However, elevated pressures increase the boiling or refluxing
point of the mixture thereby allowing the temperature to rise near the
upper range and increasing the rate of conversion. However, the rate of
conversion in the process of the present invention is so fast that
elevated temperatures near the boiling point of the mixture are not needed
thus elevated pressures are not required and not preferred.
The alcohol or glycol used in the present invention can be any alcohol or
glycol that is capable of dissolving the hydroxide or alkoxide. However,
the preferred alcohols are C.sub.l to C.sub.4 alcohols with methanol being
the most preferred and the preferred glycol is ethylene glycol.
Any polar aprotic solvent is useful in the present invention so long as the
base (alkoxide or hydroxide) in combination with the alcohol or glycol can
be dissolved therein. Examples of suitable polar aprotic solvents include
dimethyl formamide, dimethyl sulfoxide, sulfolane,
hexamethylphosphoramide, and N-methylpyrrolidone. Dimethyl sulfoxide and
N-methylpyrrolidone are most preferred due to their cost, availability,
purity, toxicity, and rate of reaction.
The alkoxides or hydroxides useful in the present invention are those that
are substantially soluble in the final solution. The preferred alkoxides
are C.sub.1 to C.sub.4 alkoxides. The preferred hydroxides are selected
from the group consisting of alkali metal hydroxides, alkaline-earth metal
hydroxides, tetra-alkyl ammonium hydroxides, and ammonium hydroxide. In
the process of the present invention, the hydroxides are preferred over
sodium hydroxide, potassium hydroxide and tetra-alkyl ammonium hydroxide.
For each mole of monomeric diacid unit in the polymer two moles of alkoxide
or hydroxide are required for a complete conversion to occur since the
acid generally has two ester bonds. However, since the rate of reaction is
proportional to the concentration of alkoxide or hydroxide in solution, it
is preferred that the alkoxide or hydroxide be in substantial molar excess
with respect to the ester bonds in the polymer so that complete conversion
of the polymer to the monomers can occur rapidly. The molar ratio of
alkoxide or hydroxide to the ester bonds in the polymer is preferably
greater than 1/1 with greater than 1.5/1 being more preferred. The upper
limit of this molar excess is limited by the solubility of the alkoxide or
hydroxide in the mixture. However, an amount in excess of this can be
present as solid in the mixture to enter solution as alkoxide or hydroxide
is depleted.
We have found that the alcohol or glycol functions to enhance the
solubility of the alkoxide or hydroxide in the polar aprotic solvent. Its
concentration in the mixture should be high enough to dissolve sufficient
hydroxide or alkoxide so that the reaction proceeds at a rapid rate.
However, excess alcohol or glycol is detrimental because it dilutes the
beneficial effect of the polar aprotic solvent.
We have found that the presence of the polar aprotic solvent enhances the
rate of reaction above that which can be achieved by the mixture of
alcohol or glycol and alkoxide or hydroxide alone. Hence, a high
concentration of polar aprotic solvent is desirable. However, hydroxides
and alkoxides are generally not as soluble in polar aprotic solvents as
they are in alcohols and glycols. If the concentration of polar aprotic
solvent becomes too large the concentration of hydroxide or alkoxide in
solution will decrease to the point where the beneficial effects of
increasing the concentration of the polar aprotic solvent will be
cancelled by a decrease in hydroxide or alkoxide concentration.
In light of what we have discovered the preferred ratio of polar aprotic
solvent to alcohol or glycol will vary depending upon which polar aprotic
solvent, alcohol or glycol, or hydroxide or alkoxide is used. In each
case, the fastest reaction rates will be determined by a compromise
between increasing the hydroxide or alkoxide solubility by the alcohol or
glycol and enhancing the rate by maximizing the concentration of the polar
aprotic solvent.
For example, when the components are as follows: dimethyl sulfoxide or
N-methylpyrrolidone as the polar aprotic solvent; sodium or potassium
hydroxide as the alkoxide or hydroxide; and methanol as the alcohol or
glycol, the preferred amounts of components are as follows: between about
10 and 99 volume % polar aprotic solvent; between about 0.5 molar and a
saturated solution of hydroxide; and between about 90 and 1 volume
methanol. The more preferred amounts of these are 20 and 95 volume %
dimethylsulfoxide or N-methylpyrrolidone and 80 and 5 volume % methanol,
saturated with hydroxide.
In some instances complete conversion of all polymer may not be desirable.
If this is desired, the polymer is simply removed from contact with the
solution when sufficient depolymerization has occurred.
The sequential addition of the components of the mixture or solution used
in the process of the present invention is not critical. However, it is
preferred that the alkoxide or hydroxide be dissolved in the alcohol or
glycol prior to the addition of the polar aprotic solvent which is then
followed by the addition of the polymer.
The container or reactor used in conducting the process of the present
invention is not critical; however, it is preferred that the process of
the present invention be conducted in a container in the presence of
agitation such as a stirred batch reactor or a continuous reactor. Though
not critical the use of a continuous reactor is the more preferred method
of employing the process of the present invention. Conducting the process
of the present invention in a continuous process is a major advantage over
high pressure reactors which must be conducted batch wise.
At the completion of the reaction (conversion) the acid monomers are
usually in the form of salts of the acids and are usually insoluble in the
reaction mixture. These insoluble salts can be recovered by any
conventional process such as by filtration. The recovered monomer salts
can be converted back to their acid form by the addition of acid.
Alternatively, if it is desired the acid monomer can be separated from the
solution by the addition of acid to precipitate the acids followed by
filtration recovery.
The process of the present invention is preferably conducted in the absence
of water. Anhydrous conditions are preferred since the rate of conversion
decreases as the amount of water increases.
The major advantage of the process of the present invention over
conventional processes is the increased rate of conversion at relatively
mild conditions of pressure and temperature.
The following examples are presented to illustrate the present invention
but are not intended to limit the reasonable scope thereof. reasonable
scope thereof.
EXAMPLES
The following examples show the unexpected rapid rate of hydrolysis of at
least partially amorphous polyester at room temperature.
EXAMPLE 1
One mL of 5 molar sodium hydroxide in methanol was added to four mL of
dimethyl sulfoxide. A 0.25 gram sample of amorphous polyethylene
terephthalate pellets (less than 1% crystallinty determined by
differential scanning calorimetry), approximately 2 mm.times.2 mm.times.3
mm, was added to the solution and the mixture was stirred at room
temperature. The experiment was repeated 12 times with an average
hydrolysis time of 55 min and a range of from 38 to 66 min. There is some
variability in the times between experiments because there is some
variability in pellet size and this has an effect on hydrolysis time.
EXAMPLE 2
The above Example 1 was repeated three times, also at room temperature,
with n-methylpyrrolidone instead of dimethyl sulfoxide. Hydrolysis times
were 140, 163, and 165 minutes.
EXAMPLE 3
Examples 1 and 2 were repeated at reflux temperature (about 120.degree. C.)
it took only 2 minutes to hydrolyze the amorphous pellets in dimethyl
sulfoxide or n-methylpyrrolidone.
EXAMPLE 4
Examples 1 and 2 were repeated with highly complete hydrolysis in dimethyl
sulfoxide or n-methylpyrrolidone at room temperature. At reflux
temperature (about 120.degree. C.) highly crystallized pellets (37%
crystallinity) hydrolyzed after 5 minutes and 7 minutes in dimethyl
sulfoxide and n-methylpyrrolidone, respectively.
EXAMPLE 5
This example demonstrates how highly crystallized polyester can be made
amorphous by melting and quenching, and thereby increase hydrolysis rate.
Crystallized polyethylene terephthalate (37% crystallinity) was melted at
271.degree. C. in a Tinius-Olsen testing machine. The melted polymer was
extruded into a 1 mm rod and quenched in water. After quenching, the
polymer was blotted with paper towels to remove excess water and allowed
to dry at room temperature for 2 hours. A 0.25 gram sample of quenched
polymer (7% crystallinity), approximately 1 mm.times.6 mm lengths, was
added to 1 mL of 5 molar sodium hydroxide in methanol and 4 mL of dimethyl
sulfoxide. The mixture was stirred at room temperature. After 47 minutes
the polymer hydrolyzed.
EXAMPLE 6
Example 5 was repeated except that the melted polymer was quenched in
dimethyl sulfoxide. After quenching, the polymer was rinsed with methanol
and blotted dry with paper towels. A 0.25 gram sample, approximately 1
mm.times.6 mm lengths, was added to 1 mL of 5 molar sodium hydroxide in
methanol and 4 mL of dimethyl sulfoxide. The mixture was stirred at room
temperature. After 26 minutes the polymer hydrolyzed.
EXAMPLE 7
Example 6 was repeated except the melted polymer was quenched in the
hydrolysis reagent (20/80 5 molar sodium hydroxide in methanol/dimethyl
sulfoxide). The polymer hydrolyzed after 26 minutes at room temperature.
The above Examples 1-7 show the dramatic increase in hydrolysis rate
between highly crystallized and essentially amorphous polyester.
The following Examples 8, 9 and 10 show the hydrolysis rate of polyester of
various crystallinities at room temperature. These data are compared in
FIG. 1.
EXAMPLE 8
In this example amorphous polyethylene terephthalate pellets, approximately
2 mm.times.2 mm.times.3 mm, were crystallized for 5 minutes at
temperatures ranging from 95.degree. C. to 155.degree. C. in 5.degree. C.
increments. This produced crystallinities ranging from 3% to 32%.
Crystallinity was measured by differential scanning calorimetry. A 0.25
gram sample of these pellets from each of these crystallization times was
added to I mL of 5 molar sodium hydroxide in methanol and 4 mL of dimethyl
sulfoxide. The mixture was stirred at room temperature. Hydrolysis times
from 44 to 320 min were observed. See FIG. 1.
EXAMPLE 9
Amorphous polyethylene terephthalate pellets, approximately 2
mm.times.2mm.times.3 mm, were also crystallized at 120.degree. C. for 5,
7, 10, 15, 20, 25 and 30 minutes. This was also repeated at 122.degree. C.
instead of 120.degree. C. for 5 and 10 minutes. These experiments
produced crystallinities ranging from 10% to 30%. Crystallinity was
measured by differential scanning calorimetry. A 0.25 gram sample of these
pellets from each of these crystallization times was added to 1 mL of 5
molar sodium hydroxide in methanol and 4 mL of dimethyl sulfoxide. The
mixture was stirred at room temperature. Hydrolysis times from 53 to 660
min were observed. See FIG. 1.
EXAMPLE 10
Amorphous polyethylene terephthalate pellets, approximately 2 mm.times.2
mm.times.3 mm, were also crystallized at 120.degree. C. for 5, 6, 7, 8, 9
and 10 minutes. This produced crystallinities ranging from 12% to 31%.
Crystallinity was measured by differential scanning calorimetry. A 0.25
gram sample of these pellets from each of these crystallization times was
added to 1 mL of 5 molar sodium hydroxide in methanol and 4 mL of dimethyl
sulfoxide. The mixture was stirred at room temperature. Hydrolysis times
of 59 to 390 min were observed. See FIG. 1.
EXAMPLE 11
This example shows the hydrolysis times of at least partially amorphous
polyester at increased temperatures using conventional hydrolysis
mixtures. Amorphous polyethylene terephthalate pellets, amorphous pellets
crystallized at 120.degree. C. for 5, 6, 7, 8, and 9 minutes, and
amorphous pellets crystallized at 180.degree. C. for 30 minutes were used.
These pellets had crystallinities ranging from 1% to 38%. Crystallinity
was measured by differential scanning calorimetry. A 0.25 gram sample of
these pellets from each of these crystallization times, approximately 2
mm.times.2 mm.times.3 mm, was added to 5 mL of 1 molar potassium hydroxide
in n-propanol. The of 1 molar potassium hydroxide in n-propanol. The
mixture was stirred at reflux, about 110.degree. C. Hydrolysis times of 7
to 39 minutes were observed. See Table 1 and FIG. 2.
EXAMPLE 12
This example was performed using the same pellets as described in Example
11. A 0.25 gram sample of these pellets from each crystallization time was
added to 1 mL of 5 molar sodium hydroxide in methanol and 4 mL dimethyl
sulfoxide. The mixture was heated at 40.degree. C. Hydrolysis times of 17
to 98 minutes were observed. This experiment was then repeated at
50.degree. C. instead of 40.degree. C. Hydrolysis times of 21 to 51
minutes were observed. Again this experiment was repeated at 80.degree. C.
instead of 40.degree. C. Hydrolysis times of 2 to 10 minutes were
observed. See Table 1.
TABLE 1
______________________________________
Hydrolysis Times at Various Crystallinities and
Temperatures
Hydrolysis
Hydrolysis
Hydrolysis
Hydrolysis
Percent Times* Times* Times* Times**
Crystal-
at 40.degree. C.
at 50.degree. C.
at 80.degree. C.
at 110.degree. C.
linity in minutes
in minutes
in minutes
in minutes
______________________________________
1% 17,23 21 2 7
12% 40,45,51 28 3 10
13% 25,31,39 26 4 9
26% 32,36 24 5 11
27% 66,67 41 7 19
31% 85,87 48 8 22
38% 94,98 51 10 39
______________________________________
*DMSO Hydrolysis Reagent
**Conventional Hydrolysis Reagent
EXAMPLE 13
This example illustrates the hydrolysis of polyethylene terephthalate in a
form other than pellets. An experiment was performed using the sidewall of
a commercial polyethylene terephthalate beverage bottle (33%
crystallinity). A 0.25 gram sample of bottle sidewall, approximately 3
mm.times.3 mm.times.1 mm, was added to 1 mL of 5 molar sodium hydroxide in
methanol and 4 mL of dimethyl sulfoxide. The mixture was stirred at room
temperature. After 80 minutes the polymer hydrolyzed.
EXAMPLE 14
This example was performed using a different polyester, amorphous
polyethylene naphthalate pellets. A 0.25 gram sample of pellets,
approximately 1 mm.times.2 mm.times.3 mm, was added to 1 mL of 5 molar
sodium hydroxide in methanol and 4 mL of dimethyl sulfoxide. The mixture
was stirred at room temperature. After 10 hours the pellets hydrolyzed.
This experiment was repeated with crystallized (37% crystallinity) instead
of amorphous pellets. After 24 hours the pellets hydrolyzed. These
experiments were repeated with approximately 4 mm.times.4 mm cylindrical
pellets instead of 1 mm.times.2 mm.times.3 mm pellets. After 15 hours and
40 hours the amorphous and crystallized (44% crystallinity) pellets
hydrolyzed, respectively. These experiments were repeated but the mixtures
were heated at reflux. At reflux temperature, about 120.degree. C., it
took 4 minutes to hydrolyze the 1 mm.times.2 mm.times.3 mm and the 4
mm.times.4 mm amorphous pellets. At reflux temperature it took 7 and 12
minutes to hydrolyze the 1 mm.times.2 mm.times.3 mm and the 4 mm.times.4
mm crystallized pellets, respectively.
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